1. Field of the Invention
The present application relates generally to agitating devices in washing machines. More particularly, the application relates to an improved vane design for such an agitating device that is able to reduce the stress experienced by the vane.
2. Description of Related Art
The general construction of clothes washing machines is well known in the art. A common type of clothes washing machine is a vertical axis washer having an agitating device and incorporating a submersion process. An agitating device can be an impeller, an agipeller, a pulsator, and infusor, or any other structure that may be used for agitating or moving clothes and fluid during the wash process. A perforated wash basket for receiving clothing is mounted in an imperforate tub. A wash liquid of detergent and water is introduced into the basket and tub. An oscillating or unidirectional agitating device is positioned within the wash basket and imparts mechanical energy to the clothing and the wash liquid.
Many agitating devices have fins, or vanes, extending radially from the bottom portion of the agitating device, just above the skirt. Examples of such structures are described in U.S. Pat. No. 6,227,014 (Euler et al.), U.S. Pat. No. 5,651,278 (Pinkowski) and U.S. Pat. No. 4,555,919 (Brenner et al.), all assigned to the assignee of the present application, the disclosure of which are incorporated by reference herein. The vanes help push the clothes in a circular direction around the center post, or barrel, of the agitating device and impart mechanical energy to the swirling wash liquid. The vanes also roll the clothes, that is, the clothes are pulled downward in the water adjacent to the agitating device, and then forced back upward along the inside of the basket.
Traditional vanes were stiff and essentially functioned as a pump. Stiff-vaned agitating devices were limited in the amount of clothes that could be circulated without overheating the drive motor of the drive system of the washing machine. Flexible vanes were developed to increase the amount of clothes that could be washed while staying within the torque level of the drive system of the washing machine. A flexible vane would flex under a heavy load, and upon reversal of stroke direction, the bent vane would quickly flip and bend in the opposite direction, causing an increased push on the garments. The direction of push could be controlled by the hinge point of the vane, the hinge point being the first point where the vane is attached to the skirt of an agitating device moving from the tip of the vane in a direction toward the barrel of the agitating device. For vanes which do not attach to the skirt, the hinge point is the first point at which the vane attaches to the barrel. Thus it was possible to push the clothes outward along the bottom of the wash basket and also impart an upward momentum if desired. The combined effect of the bent vane's surface area and the directional push upon reversal of the stroke direction allowed for increased clothes load washing capacity with the same drive system torque.
Stress is exerted on the vanes as they move the water and clothes in a reciprocating circular direction. The vanes must flex in multiple directions to absorb the stress caused by circulating water and moving clothes without breaking off during the wash process. Stress is concentrated at the hinge point because of the abrupt change in geometry between the base of the vane and tip of the vane.
The stress level in a vane may be increased through two factors. First, changes in vane technology may increase the stress within a vane. For example, over the years, vanes have been made thinner, their outer tips extended further away from the center shaft, and stress loading concentrated near the hinge points of the vanes. Secondly, the increased effectiveness of the vanes has allowed for an increased amount of clothing in the wash process, which in turn increased the stress on the vane.
One alternative to reduce the stress in a vane of an agitating device is to use a blended material or a two-part vane system. A flexible material can be added to the vane during the molding process to change the durableness of the vane. An alternate flexible material may be used to mold the vane tip while the remainder of the agitating device is made out of a stiff material. However, both of these processes significantly increase the cost and complexity of the manufacturing process.
Thus, there must be a balance between the strength and the flexibility of the vanes because they must be strong enough not to break but also flexible enough to reduce fabric abrasion and to promote wash performance. Accordingly, it is desirable to develop a vane blade design that will lower the stress level on the hinge point of the vane to a desirable range to minimize breakage while still being flexible enough to reduce fabric abrasion.